System in Package (SIP) technology allows the integration into one package of the multiple die, devices and components needed to make up a system. As more diverse technologies are used to manufacture die, SIPs are becoming useful for including and integrating all these various dies into a system or subsystem. These systems often have a need to communicate with other systems or networks and are including components that transmit and receive radio frequency (RF) signals (so-called “wireless components”).
In SIP molded packages, different types of devices and components may be assembled on a substrate prior to encapsulation. These devices and components may be passive devices such as capacitors, inductors and resistors, and bare die or pre-packaged IC devices such as DRAM, CPU or other ICs. Typically, a molded SIP is encapsulated as part of the final packaging process. The encapsulating material, often referred to as a molding compound, can be a thermosetting plastic material with fillers, such as silica, in it. In this case, when the molding compound is heated to a certain temperature, the molding compound melts and attains a very low viscosity for a short period of time, and then it gels and hardens. It is important that while it is in liquid form it completely fill the package mold cavity. In the case of a SIP, the liquid form should not only fill the mold cavity but also fill around and below the components that have been previously mounted on a SIP substrate. In general, all the passives and IC packages may be mounted on a SIP substrate such that each of these devices and components have sufficient clearance above the SIP substrate for encapsulating material (hereinafter “encapsulant”) to flow between the bottom of the device/component and the substrate. This allows the encapsulant or molding compound to flow underneath the device/component and all around it to form a void free SIP package. Otherwise, the resulting SIP molded package may contain voids and air gaps, which may cause several problems, such as condensation of moisture and related degradation of a package, popping of the package during surface mount, cracking, corrosion and current leakage resulting from corrosion. Depending on the chosen encapsulant, voids may accumulate moisture which will create unwanted electrical paths, thereby reducing the expected life of a system. In system applications which are exposed to high pressure or vacuum environments, voids may further create a pressure stabilization problem for the system.
The inclusion of components generating a radio frequency (RF) signal (e.g., a wireless communications component) in a SIP can present a challenge for the encapsulation process. In some wireless systems on printed circuit boards (PCBs) that are not encapsulated, metal shields (or cans) are sometimes placed around the wireless component(s) to shield other components on the PCB from the RF signals. This radio frequency emission shielding can help prevent electro-magnetic interference (EMI) with other components of the system. However, the metal shields (or cans) placed on the PCB would make it difficult to allow a molding compound to fill the gap between the metal EMI can and wireless components, and in particular, to do so without any voids or air gaps while sufficiently shielding of components of the system.
Accordingly, there remains a need for effective ways of providing RF shielding for components in a molded package from EMI.